The present invention relates generally to pilot guidance instrumentation and more particularly, to a method and apparatus for automatically operating such instrumentation to assist the pilot in executing a thrust cutback maneuver for abating jet engine noise.
A number of methods have been proposed for reducing noise during the post-takeoff climb over residential and business communities in the vicinity of airports. Some of these have been partially successful.
Among the numerous prior proposals, the following were believed, at least initially, to have promise: reducing thrust to a precomputed level at a specified time from takeoff; accelerating to an above normal climbing speed and then automatically retracting flaps and concurrently reducing thrust; and reducing thrust at preestablished altitudes. Later studies have shown that each of these has one or more faults. Reducing thrust to a precomputed level results in inconsistencies in the flight paths of like-model aircraft, due to variation in performance. The implementation of automatic flap retraction is complex and costly, and time required to execute the maneuver is not always compatible with the community location. Pre-established altitudes, as benchmarks for the noise abatement maneuver, has resulted in thrust cutback times that are frequently not coincident with the boundaries of the community.
One proposal for overcoming this synchronization problem is to cut thrust (by the predetermined amount) at a specified time from the start of the takeoff run. Using times that are arrived at from variables including: aircraft type and model, airport runway and departure flight path, a reasonably accurate coincidence has been achieved between the position of the aircraft at thrust cutback and the community boundary. The acceleration and attained speed of aircraft, during the takeoff run and initial climb are sufficiently uniform from flight-to-flight so that the specified cutback time (which may be adjusted for wind direction and velocity) is a predictable distance of travel (ground distance) from the start of the runway. For a given departure path from a given runway, the cutback time is selected to yield a travel distance matching the distance to the closest boundary of the community. However even using this technique, the results have not been satisfactory because of the above-noted inconsistencies in the flight path when the thrust is reduced to some precomputed level.
There are other techniques, not enumerated above, that have been proposed, but again found undesirable for such reasons as: an increase in workload of the pilot; a decrease in controllability of the aircraft; and/or a lack of pilot confidence in the maneuver or in the instrumentation that governs the maneuver.
Accordingly, it is object of the present invention to provide method and apparatus for automatically generating and visually displaying steering commands that direct the pilot in executing a thrust cutback maneuver and assist him in piloting the aircraft over the community at the noise abated, lower thrust level.
A further object is to generate and display such commands at thrust cutback and restoration times that are coincident with the flight of the aircraft over the community boundaries.
Also, it is an object to provide method and apparatus for directing a noise abatement maneuver that does not substantially increase the preflight and in-flight workloads of the pilot. Further objects are to: instill pilot confidence in the safety and effectiveness of the maneuver; insure full aircraft controllability and safe stall margins; insure the continuance of a positive, safe climb (no chance for loss of altitude); keep to a minimum, the cost of implementation; and use apparatus that is compatible with existing pilot guidance systems.